Water Rocket Forum

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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

WRA2 wrote:What about allowing bottles that weren't soft drink bottles into the reinforced competition (unmodified). Since the bottle would be reinforced, other types of bottles could be used (shampoo bottles, water bottles, iced tea bottles, ketchup bottles and the list goes on and on). That way teams would have a much bigger choice in bottle shape.

I must say, I've been misreading the current rules. I thought we already were saying "beverage bottle", and didn't realize "soft drink" was still specified. I certainly think things like iced tea and water bottles should be allowed- most of them are made from the same stretch-blow-moulded PET as pop bottles, but sometimes in different formats. I don't see how ketchup bottles would be useful, and I don't see how we would word it to allow those kinds of things without making it too open. My suggestion would be "non-alcoholic plastic beverage bottle". I'm not too concerned about the non-alcoholic part, but some of those bottles are a lot thicker, and allowing them would put under-aged competitors at a slight disadvantage.

Hi Alex,
I think we addressed the "thicker walled" bottles already. For the unreinforced class the thicker bottle will be at a weight disadvantage since we have a pressure limit of 100PSI. For the reinforced class, competitors are allowed to reinforce their bottles as they see fit using approved materials so there is no advantage to using thicker walled bottles either.

I used ketchup bottles as an example of a non-beverage container to give the competitor more choices as to bottle shape. Who knows, maybe a team will discover some new aspect or flight characteristic by using a rectangular shaped shampoo bottle (in the reinforced bottle competition). For the unreinforced we should stick to beverage containers and maybe limit it to only containers designed for carbonated beverages as some of the water bottles I have seen are pretty thin walled and may not even make 100 PSI (or is this a self correcting problem since unsuitible bottles would "eliminate themselves" anyways.

I also want to make it more clear that the use of metal parts either in the construction of or to reinforce the pressure vessel (depending on class) or attached to the pressure vessel is dangerous and not allowed. I have see a few examples where a team will attach metal guide lugs and or braces to their rocket. Metal parts should not be attached to any pressurized portion of the rocket. But it also need to be clear that metal parts in a payload bay that is separate from the pressurized portion is allowed (electronics, springs, wires, levers, plungers, batteries etc.)

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association